/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.hasor.web.upload;
import net.hasor.web.FileUploadException;
import net.hasor.web.upload.util.Streams;

import java.io.*;

import static java.lang.String.format;
import static net.hasor.web.FileUploadException.UploadErrorCodes.*;
/**
 * <p> Low level API for processing file uploads.
 *
 * <p> This class can be used to process data streams conforming to MIME
 * 'multipart' format as defined in
 * <a href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a>. Arbitrarily
 * large amounts of data in the stream can be processed under constant
 * memory usage.
 *
 * <p> The format of the stream is defined in the following way:<br>
 *
 * <code>
 *   multipart-body := preamble 1*encapsulation close-delimiter epilogue<br>
 *   encapsulation := delimiter body CRLF<br>
 *   delimiter := "--" boundary CRLF<br>
 *   close-delimiter := "--" boundary "--"<br>
 *   preamble := &lt;ignore&gt;<br>
 *   epilogue := &lt;ignore&gt;<br>
 *   body := header-part CRLF body-part<br>
 *   header-part := 1*header CRLF<br>
 *   header := header-name ":" header-value<br>
 *   header-name := &lt;printable ascii characters except ":"&gt;<br>
 *   header-value := &lt;any ascii characters except CR &amp; LF&gt;<br>
 *   body-data := &lt;arbitrary data&gt;<br>
 * </code>
 *
 * <p>Note that body-data can contain another mulipart entity.  There
 * is limited support for single pass processing of such nested
 * streams.  The nested stream is <strong>required</strong> to have a
 * boundary token of the same length as the parent stream (see {@link
 * #setBoundary(byte[])}).
 *
 * <p>Here is an example of usage of this class.<br>
 *
 * <pre>
 *   try {
 *     MultipartStream multipartStream = new MultipartStream(input, boundary);
 *     boolean nextPart = multipartStream.skipPreamble();
 *     OutputStream output;
 *     while(nextPart) {
 *       String header = multipartStream.readHeaders();
 *       // process headers
 *       // create some output stream
 *       multipartStream.readBodyData(output);
 *       nextPart = multipartStream.readBoundary();
 *     }
 *   } catch(MultipartStream.MalformedStreamException e) {
 *     // the stream failed to follow required syntax
 *   } catch(IOException e) {
 *     // a read or write error occurred
 *   }
 * </pre>
 *
 * @version $Id: MultipartStream.java 1745065 2016-05-22 14:56:37Z britter $
 */
class MultipartStream {
    // ----------------------------------------------------- Manifest constants
    /** The Carriage Return ASCII character value. */
    public static final    byte   CR                   = 0x0D;
    /** The Line Feed ASCII character value. */
    public static final    byte   LF                   = 0x0A;
    /** The dash (-) ASCII character value. */
    public static final    byte   DASH                 = 0x2D;
    /** The maximum length of <code>header-part</code> that will be processed (10 kilobytes = 10240 bytes.). */
    public static final    int    HEADER_PART_SIZE_MAX = 10240;
    /** The default length of the buffer used for processing a request. */
    protected static final int    DEFAULT_BUFSIZE      = 4096;
    /** A byte sequence that marks the end of <code>header-part</code> (<code>CRLFCRLF</code>). */
    protected static final byte[] HEADER_SEPARATOR     = { CR, LF, CR, LF };
    /** A byte sequence that that follows a delimiter that will be followed by an encapsulation (<code>CRLF</code>). */
    protected static final byte[] FIELD_SEPARATOR      = { CR, LF };
    /** A byte sequence that that follows a delimiter of the last encapsulation in the stream (<code>--</code>). */
    protected static final byte[] STREAM_TERMINATOR    = { DASH, DASH };
    /** A byte sequence that precedes a boundary (<code>CRLF--</code>). */
    protected static final byte[] BOUNDARY_PREFIX      = { CR, LF, DASH, DASH };
    // ----------------------------------------------------------- Data members
    /** The input stream from which data is read. */
    private final InputStream input;
    /** The length of the boundary token plus the leading <code>CRLF--</code>. */
    private       int         boundaryLength;
    /** The amount of data, in bytes, that must be kept in the buffer in order to detect delimiters reliably. */
    private       int         keepRegion;
    /** The byte sequence that partitions the stream. */
    private       byte[]      boundary;
    /** The length of the buffer used for processing the request. */
    private final int         bufSize;
    /** The buffer used for processing the request. */
    private final byte[]      buffer;
    /** The index of first valid character in the buffer. <br> 0 <= head < bufSize */
    private       int         head;
    /** The index of last valid character in the buffer + 1. <br> 0 <= tail <= bufSize */
    private       int         tail;
    /** The content encoding to use when reading headers. */
    private       String      headerEncoding;
    // ----------------------------------------------------------- Constructors
    /**
     * <p> Constructs a <code>MultipartStream</code> with a custom size buffer.
     *
     * <p> Note that the buffer must be at least big enough to contain the
     * boundary string, plus 4 characters for CR/LF and double dash, plus at
     * least one byte of data.  Too small a buffer size setting will degrade
     * performance.
     *
     * @param input    The <code>InputStream</code> to serve as a data source.
     * @param boundary The token used for dividing the stream into
     *                 <code>encapsulations</code>.
     * @param bufSize  The size of the buffer to be used, in bytes.
     * @throws IllegalArgumentException If the buffer size is too small
     * @since 1.3.1
     */
    public MultipartStream(InputStream input, byte[] boundary, int bufSize) {
        if (boundary == null) {
            throw new IllegalArgumentException("boundary may not be null");
        }
        // We prepend CR/LF to the boundary to chop trailing CR/LF from body-data tokens.
        this.boundaryLength = boundary.length + BOUNDARY_PREFIX.length;
        if (bufSize < this.boundaryLength + 1) {
            throw new IllegalArgumentException("The buffer size specified for the MultipartStream is too small");
        }
        this.input = input;
        this.bufSize = Math.max(bufSize, boundaryLength * 2);
        this.buffer = new byte[this.bufSize];
        this.boundary = new byte[this.boundaryLength];
        this.keepRegion = this.boundary.length;
        System.arraycopy(BOUNDARY_PREFIX, 0, this.boundary, 0, BOUNDARY_PREFIX.length);
        System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);
        head = 0;
        tail = 0;
    }
    /**
     * <p> Constructs a <code>MultipartStream</code> with a default size buffer.
     * @param input    The <code>InputStream</code> to serve as a data source.
     * @param boundary The token used for dividing the stream into <code>encapsulations</code>.
     * @see #MultipartStream(InputStream, byte[], int)
     */
    MultipartStream(InputStream input, byte[] boundary) {
        this(input, boundary, DEFAULT_BUFSIZE);
    }
    // --------------------------------------------------------- Public methods
    /**
     * Retrieves the character encoding used when reading the headers of an
     * individual part. When not specified, or <code>null</code>, the platform default encoding is used.
     * @return The encoding used to read part headers.
     */
    public String getHeaderEncoding() {
        return headerEncoding;
    }
    /**
     * Specifies the character encoding to be used when reading the headers of
     * individual parts. When not specified, or <code>null</code>, the platform
     * default encoding is used.
     * @param encoding The encoding used to read part headers.
     */
    public void setHeaderEncoding(String encoding) {
        headerEncoding = encoding;
    }
    /**
     * Reads a byte from the <code>buffer</code>, and refills it as necessary.
     * @return The next byte from the input stream.
     * @throws IOException if there is no more data available.
     */
    public byte readByte() throws IOException {
        // Buffer depleted ?
        if (head == tail) {
            head = 0;
            // Refill.
            tail = input.read(buffer, head, bufSize);
            if (tail == -1) {
                // No more data available.
                throw new IOException("No more data is available");
            }
        }
        return buffer[head++];
    }
    /**
     * Skips a <code>boundary</code> token, and checks whether more
     * <code>encapsulations</code> are contained in the stream.
     * @return <code>true</code> if there are more encapsulations in this stream; <code>false</code> otherwise.
     * @throws FileUploadException if the stream ends unexpectedly or fails to follow required syntax.
     */
    public boolean readBoundary() throws IOException {
        byte[] marker = new byte[2];
        boolean nextChunk = false;
        head += boundaryLength;
        marker[0] = readByte();
        if (marker[0] == LF) {
            // Work around IE5 Mac bug with input type=image.
            // Because the boundary delimiter, not including the trailing CRLF, 
            // must not appear within any file (RFC 2046, section 5.1.1),
            // we know the missing CR is due to a buggy browser rather than a file 
            // containing something similar to a boundary.
            return true;
        }
        marker[1] = readByte();
        if (arrayequals(marker, STREAM_TERMINATOR, 2)) {
            nextChunk = false;
        } else if (arrayequals(marker, FIELD_SEPARATOR, 2)) {
            nextChunk = true;
        } else {
            throw new FileUploadException(MalformedStreamException, "Unexpected characters follow a boundary");
        }
        return nextChunk;
    }
    /**
     * <p>Changes the boundary token used for partitioning the stream.
     * <p>This method allows single pass processing of nested multipart streams.
     * <p>The boundary token of the nested stream is <code>required</code> to be of the same length as the boundary token in parent stream.
     * <p>Restoring the parent stream boundary token after processing of a nested stream is left to the application.
     * @param boundary The boundary to be used for parsing of the nested stream.
     * @throws FileUploadException if the <code>boundary</code> has a different length than the one being currently parsed.
     */
    public void setBoundary(byte[] boundary) throws FileUploadException {
        if (boundary.length != boundaryLength - BOUNDARY_PREFIX.length) {
            throw new FileUploadException(IllegalBoundaryException, "The length of a boundary token can not be changed");
        }
        System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);
    }
    /**
     * <p>Reads the <code>header-part</code> of the current
     * <code>encapsulation</code>.
     * <p>Headers are returned verbatim to the input stream, including the
     * trailing <code>CRLF</code> marker. Parsing is left to the application.
     * <p><strong>TODO</strong> allow limiting maximum header size to protect against abuse.
     *
     * @return The <code>header-part</code> of the current encapsulation.
     * @throws FileUploadException if the stream ends unexpectedly.
     */
    public String readHeaders() throws IOException {
        int i = 0;
        byte b;
        // to support multi-byte characters
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int size = 0;
        while (i < HEADER_SEPARATOR.length) {
            try {
                b = readByte();
            } catch (IOException e) {
                throw e;
            }
            if (++size > HEADER_PART_SIZE_MAX) {
                String logMEssage = format("Header section has more than %s bytes (maybe it is not properly terminated)", Integer.valueOf(HEADER_PART_SIZE_MAX));
                throw new FileUploadException(MalformedStreamException, logMEssage);
            }
            if (b == HEADER_SEPARATOR[i]) {
                i++;
            } else {
                i = 0;
            }
            baos.write(b);
        }
        String headers = null;
        if (headerEncoding != null) {
            try {
                headers = baos.toString(headerEncoding);
            } catch (UnsupportedEncodingException e) {
                // Fall back to platform default if specified encoding is not supported.
                headers = baos.toString();
            }
        } else {
            headers = baos.toString();
        }
        return headers;
    }
    /**
     * <p>Reads <code>body-data</code> from the current <code>encapsulation</code> and writes its contents into the output <code>Stream</code>.
     * <p>Arbitrary large amounts of data can be processed by this method using a constant size buffer. 
     * @param output The <code>Stream</code> to write data into. May be null, in which case this method is equivalent to {@link #discardBodyData()}.
     * @return the amount of data written.
     * @throws FileUploadException if the stream ends unexpectedly.
     * @throws IOException              if an i/o error occurs.
     */
    public int readBodyData(OutputStream output) throws IOException {
        final InputStream istream = newInputStream();
        return (int) Streams.copy(istream, output, false);
    }
    /**
     * Creates a new {@link ItemInputStream}.
     * @return A new instance of {@link ItemInputStream}.
     */
    ItemInputStream newInputStream() {
        return new ItemInputStream();
    }
    /**
     * <p> Reads <code>body-data</code> from the current
     * <code>encapsulation</code> and discards it.
     *
     * <p>Use this method to skip encapsulations you don't need or don't understand.
     *
     * @return The amount of data discarded.
     * @throws FileUploadException if the stream ends unexpectedly.
     * @throws IOException         if an i/o error occurs.
     */
    public int discardBodyData() throws IOException {
        return readBodyData(null);
    }
    /**
     * Finds the beginning of the first <code>encapsulation</code>.
     * @return <code>true</code> if an <code>encapsulation</code> was found in the stream.
     *
     * @throws IOException if an i/o error occurs.
     */
    public boolean skipPreamble() throws IOException {
        // First delimiter may be not preceeded with a CRLF.
        System.arraycopy(boundary, 2, boundary, 0, boundary.length - 2);
        boundaryLength = boundary.length - 2;
        try {
            // Discard all data up to the delimiter.
            discardBodyData();
            // Read boundary - if succeeded, the stream contains an encapsulation.
            return readBoundary();
        } catch (FileUploadException e) {
            if (e.getErrorCode() == MalformedStreamException) {
                return false;
            }
            throw e;
        } finally {
            // Restore delimiter.
            System.arraycopy(boundary, 0, boundary, 2, boundary.length - 2);
            boundaryLength = boundary.length;
            boundary[0] = CR;
            boundary[1] = LF;
        }
    }
    /**
     * Compares <code>count</code> first bytes in the arrays <code>a</code> and <code>b</code>.
     * @param a     The first array to compare.
     * @param b     The second array to compare.
     * @param count How many bytes should be compared.
     *
     * @return <code>true</code> if <code>count</code> first bytes in arrays
     *         <code>a</code> and <code>b</code> are equal.
     */
    public static boolean arrayequals(byte[] a, byte[] b, int count) {
        for (int i = 0; i < count; i++) {
            if (a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }
    /**
     * Searches for a byte of specified value in the <code>buffer</code>,
     * starting at the specified <code>position</code>.
     *
     * @param value The value to find.
     * @param pos   The starting position for searching.
     *
     * @return The position of byte found, counting from beginning of the
     *         <code>buffer</code>, or <code>-1</code> if not found.
     */
    protected int findByte(byte value, int pos) {
        for (int i = pos; i < tail; i++) {
            if (buffer[i] == value) {
                return i;
            }
        }
        return -1;
    }
    /**
     * Searches for the <code>boundary</code> in the <code>buffer</code>
     * region delimited by <code>head</code> and <code>tail</code>.
     *
     * @return The position of the boundary found, counting from the
     *         beginning of the <code>buffer</code>, or <code>-1</code> if not found.
     */
    protected int findSeparator() {
        int first;
        int match = 0;
        int maxpos = tail - boundaryLength;
        for (first = head; first <= maxpos && match != boundaryLength; first++) {
            first = findByte(boundary[0], first);
            if (first == -1 || first > maxpos) {
                return -1;
            }
            for (match = 1; match < boundaryLength; match++) {
                if (buffer[first + match] != boundary[match]) {
                    break;
                }
            }
        }
        if (match == boundaryLength) {
            return first - 1;
        }
        return -1;
    }
    /** An {@link InputStream} for reading an items contents. */
    public class ItemInputStream extends InputStream implements net.hasor.web.upload.util.Closeable {
        /** The number of bytes, which have been read so far. */
        private long    total;
        /** The number of bytes, which must be hold, because they might be a part of the boundary. */
        private int     pad;
        /** The current offset in the buffer. */
        private int     pos;
        /** Whether the stream is already closed. */
        private boolean closed;
        /** Creates a new instance. */
        ItemInputStream() {
            findSeparator();
        }
        /** Called for finding the separator. */
        private void findSeparator() {
            pos = MultipartStream.this.findSeparator();
            if (pos == -1) {
                if (tail - head > keepRegion) {
                    pad = keepRegion;
                } else {
                    pad = tail - head;
                }
            }
        }
        /** Returns the number of bytes, which have been read by the stream.
         * @return Number of bytes, which have been read so far.
         */
        public long getBytesRead() {
            return total;
        }
        /**
         * Returns the number of bytes, which are currently available, without blocking.
         * @return Number of bytes in the buffer.
         */
        @Override
        public int available() {
            if (pos == -1) {
                return tail - head - pad;
            }
            return pos - head;
        }
        /** Offset when converting negative bytes to integers. */
        private static final int BYTE_POSITIVE_OFFSET = 256;
        /**
         * Returns the next byte in the stream.
         * @return The next byte in the stream, as a non-negative integer, or -1 for EOF.
         * @throws IOException An I/O error occurred.
         */
        @Override
        public int read() throws IOException {
            if (closed) {
                throw new FileUploadException(ItemSkippedException);
            }
            if (available() == 0 && makeAvailable() == 0) {
                return -1;
            }
            ++total;
            int b = buffer[head++];
            if (b >= 0) {
                return b;
            }
            return b + BYTE_POSITIVE_OFFSET;
        }
        /**
         * Reads bytes into the given buffer.
         * @param b The destination buffer, where to write to.
         * @param off Offset of the first byte in the buffer.
         * @param len Maximum number of bytes to read.
         * @return Number of bytes, which have been actually read, or -1 for EOF.
         * @throws IOException An I/O error occurred.
         */
        @Override
        public int read(byte[] b, int off, int len) throws IOException {
            if (closed) {
                throw new FileUploadException(ItemSkippedException);
            }
            if (len == 0) {
                return 0;
            }
            int res = available();
            if (res == 0) {
                res = makeAvailable();
                if (res == 0) {
                    return -1;
                }
            }
            res = Math.min(res, len);
            System.arraycopy(buffer, head, b, off, res);
            head += res;
            total += res;
            return res;
        }
        /**
         * Closes the input stream.
         * @throws IOException An I/O error occurred.
         */
        @Override
        public void close() throws IOException {
            close(false);
        }
        /**
         * Closes the input stream.
         * @param pCloseUnderlying Whether to close the underlying stream (hard close)
         * @throws IOException An I/O error occurred.
         */
        public void close(boolean pCloseUnderlying) throws IOException {
            if (closed) {
                return;
            }
            if (pCloseUnderlying) {
                closed = true;
                input.close();
            } else {
                for (; ; ) {
                    int av = available();
                    if (av == 0) {
                        av = makeAvailable();
                        if (av == 0) {
                            break;
                        }
                    }
                    skip(av);
                }
            }
            closed = true;
        }
        /**
         * Skips the given number of bytes.
         * @param bytes Number of bytes to skip.
         * @return The number of bytes, which have actually been skipped.
         * @throws IOException An I/O error occurred.
         */
        @Override
        public long skip(long bytes) throws IOException {
            if (closed) {
                throw new FileUploadException(ItemSkippedException);
            }
            int av = available();
            if (av == 0) {
                av = makeAvailable();
                if (av == 0) {
                    return 0;
                }
            }
            long res = Math.min(av, bytes);
            head += res;
            return res;
        }
        /**
         * Attempts to read more data.
         * @return Number of available bytes
         * @throws IOException An I/O error occurred.
         */
        private int makeAvailable() throws IOException {
            if (pos != -1) {
                return 0;
            }
            // Move the data to the beginning of the buffer.
            total += tail - head - pad;
            System.arraycopy(buffer, tail - pad, buffer, 0, pad);
            // Refill buffer with new data.
            head = 0;
            tail = pad;
            for (; ; ) {
                int bytesRead = input.read(buffer, tail, bufSize - tail);
                if (bytesRead == -1) {
                    // The last pad amount is left in the buffer. Boundary can't be in there so signal an error condition.
                    final String msg = "Stream ended unexpectedly";
                    throw new FileUploadException(MalformedStreamException, msg);
                }
                tail += bytesRead;
                findSeparator();
                int av = available();
                if (av > 0 || pos != -1) {
                    return av;
                }
            }
        }
        /**
         * Returns, whether the stream is closed.
         * @return True, if the stream is closed, otherwise false.
         */
        public boolean isClosed() {
            return closed;
        }
    }
}